1. Field of the Invention
This invention relates to devices and apparatus for suspending tubing, and coiled tubing in particular, in an oil or gas well and more particularly, to a manually-operated coiled tubing hanger assembly for suspending coiled or conventional tubing in a well without the necessity of "killing" the well. The coiled tubing hanger assembly of this invention is characterized by multiple, mechanically-assisted, tapered and collectively conically-shaped slip segments constrained to operate in concert by a retainer ring and positioned in the correspondingly tapered slip bowl of a specially designed tubing head, which includes a top bonnet, a midsection and a lower body, typically bolted together. In a preferred embodiment the slips rest on a rack cylinder having a central longitudinal bore and typically fitted with lands and grooves, which lands and grooves engage a pinion gear attached to one end of a slip-operating mechanism to facilitate manual vertical movement of the rack cylinder, and thus the slips, in the midsection. This action effects selective release and engagement of the slips with a segment of tubing such as coiled tubing, extending through the tubing head, to control insertion and retrieval of the tubing into and from an underlying well. A pack-off assembly is located in the lower body of the tubing head for sealing the coiled tubing hanger assembly against well pressure and the packing seal in the pack-off assembly is facilitated by tapered or bevelled-end pack-off screws extending radially through the lower body to engage the bevelled pack-off plate above the seals in the pack-off assembly. The conical base of a slip cone engages the correspondingly-shaped top inside surfaces of the slips when seated in the midsection and the top bonnet, to maintain the slips in proper functional orientation in the tubing head. A cylinder landing ring is seated in the midsection and lower body interface to limit downward travel of the rack cylinder.
As the downhole pressure in oil and gas wells decreases with time, it is sometimes desirable or necessary to insert tubing in the well to provide a mechanism for more readily removing fluids from the well and prolong the life of the well. Traditionally, it has been necessary to "kill" the well or terminate production by application of hydrostatic pressure in the well, to achieve this objective. A well is "killed" or production is terminated from the well, typically by pumping a fluid such as water into the producing interval to create a hydrostatic head of sufficient magnitude in the well to overcome the well pressure, thereby terminating production. One of the problems inherent in "killing" a producing well which has relatively low pressure, is the difficulty and sometimes impossibility, of restoring the well to production after the desired swabbing, cleaning or workover operation has been accomplished. These and other well maintenance operations are expensive, generally because of the time required to effect such steps as removing the "christmas tree", setting up the necessary apparatus for maintaining the well, placing tubing in the well, (under circumstances where such tubing is deemed necessary), placing a tubing head on the master valve, setting the conventional, usually gravity-operated slip segments and the necessary packing, replacing the "christmas tree" and subsequently attempting to bring the well back into production. If the well cannot be brought back into production, then the time and money expended in the effort has obviously been wasted.
The use of coiled tubing as an alternative to running a production tubing string has received increased attention through the years. Under circumstances where the coiled tubing can be manipulated in a tubing hanger and anchor assembly which is compatible with the needs of the operator, many of the well operating objectives can be accomplished. This is especially true under circumstances where the coiled tubing is designed to keep marginal wells unloaded. For example, the coiled tubing can be used as a cycling string to delay or replace the need for much more expensive or less efficient forms of artificial lift. Furthermore, the coiled tubing can be secured in the slip bowl of the coiled tubing anchor assembly with a close tolerance and can be quickly and easily adjusted up or down, as desired. Other advantages of running coiled tubing in the place of conventional tubing strings in wells will be hereinafter apparent.
2. Description of the Prior Art
Gravity-operated slip assemblies and related equipment of various design have long been employed in the oilfield for suspending pipe and tubing in oil and gas wells. Such assemblies usually consist of multiple, segmented wedges which are tapered and are provided with horizontally-extending teeth located on curved inner surfaces, which teeth are designed to engage and cut into the pipe or tubing to prevent relative movement between the tubing and the slips. The slips usually include several segments which together conform to a tapered, usually conical slip bowl provided in a tubing head and facilitate engagement of the slips by gravity radially about the pipe or tubing when the slips are released inside the slip bowl responsive to contact between the tapered outside surfaces of the slips and the slip bowl in the tubing head. Lowering of the pipe or tubing after release of the slips results in a radial compressive force which urges the segment teeth against the pipe or tubing until the teeth cut into the pipe or tubing wall sufficiently to support the weight of the tubing in the tubing head. The teeth provided in the curved inner face of each slip segment are configured and oriented to engage and cut into the pipe or tubing in an optimum manner, in order to prevent relative movement between the slip segments and the suspended pipe or tubing.
Various devices have long been known in the prior art for supporting casing and tubing in oil and gas wells. An early "Casing Head" is detailed in U.S. Pat. No. 1,400,940, dated Dec. 20, 1921, to C. S. Clarke. The Clarke device includes a clamping member which is adapted to grip a pipe by wedging into engagement with the pipe, responsive to the weight of the pipe. A "Safety Clamp For Diamond Drill Rods" is detailed in U.S. Pat. No. 1,458,906, to N. W. Morisette. The device includes a clamp device having a housing fitted with a sliding element having teeth and a rotating clamping apparatus that selectively engages the teeth to clamp a workstock extending through a bore defined by the teeth. U.S. Pat. No. 1,575,998, dated Mar. 9, 1926, to W. H. McKissick, details a "Tubing Spider" which includes an annular carrier from which slips are suspended, with an operating mechanism for elevating the carrier, such that the slips are retracted into the body of the spider relatively outwardly of the depending guide flange into selective contact with tubing extending through the device. U.S. Pat. No. 2,071,637, dated Feb. 23, 1937, to M. P. Laurent, details a "Slip" characterized by a bushing shaped to fit within a rotary table and a downwardly-tapered, circular seat in the bushing, along with multiple downwardly and inwardly-inclined slideways recessed into the seat of the bushing and slips having outer inclined faces fitting within the slideways, the inner faces of the slips also have a mortised recess opening at the top. An insert having a tenon thereon engages each of the recesses. U.S. Pat. No. 2,896,292, dated Jul. 28, 1959, to R. B. Kinzbach, details an "Automatic Tubing Spider Assembly" which includes a spider body formed with radially-disposed wings having recesses to receive corresponding, radially-movable gripping members pivotally carried on links which are pivotally secured to the spider body. The links are shaped in the configuration of cams provided in camming engagement with the gripping members and with the spider body, thus providing supporting connection between the gripping members and the spider body, as well as between the gripping members and the tubing, when the members sustain a load. U.S. Pat. No. 3,791,661, dated Feb. 12, 1974, to Charles E. Giles, details a "Collet and Collet Fixture". The collet and collet fixture allows an adjustment in the height of a workpiece held in the collet. The collet is locked into position from the bottom by the fixture, providing a secure positioning of the collet and accurate machining of the workpiece. Other patents detailing typical slip-operated tubing head designs are U.S. Pat. No. 3,287,035, dated Nov. 22, 1966, to Greenwood; U.S. Pat. No. 4,334,342, dated Jun. 15, 1982, to Hall; U.S. Pat. No. 4,326,587, dated Apr. 27, 1987, to Gauthier, et al; U.S. Pat. No. 4,554,971, dated Nov. 26, 1985, to Cobb; and U.S. Pat. No. 4,646,827, dated Mar. 3, 1989, also to Cobb.
It is an object of this invention to provide a new and improved tubing hanger assembly for suspending tubing in an oil or gas well using a mechanically-assisted slip assembly to selectively engage and disengage the tubing.
Another object of this invention is to provide a tubing hanger assembly for running tubing, and coiled tubing in particular, in an oil or gas well, which assembly is characterized by multiple, bevelled, collectively conical slip segments loosely connected by a retainer ring and mounted in the correspondingly conical throat of a tubing head. A rack element such as a cylindrical rack cylinder is located in the tubing head beneath the slips and is fitted with teeth or lands and grooves engaged by a pinion gear attached to a slip-operating mechanism, for selectively manipulating the cylinder and the slips upwardly and downwardly in the tubing head and facilitating controlled engagement and release of the slip segments in the slip bowl of the tubing head with tubing placed in the well.
Another object of this invention is to provide a new and improved coiled tubing hanger assembly for use in a specially designed tubing head to suspend coiled tubing in oil and gas wells, typically without "killing" the wells, which hanger assembly includes as the first element, multiple, tapered slip segments clustered in a slip assembly by a retainer ring and disposed in the tapered slip bowl of the tubing head, a cylindrical rack cylinder located in the tubing head beneath the slip segments and engaging the slip segments, teeth or lands and grooves provided on the rack cylinder for engagement by a pinion gear attached to an externally-projecting slip-operating mechanism, to facilitate selective rotation of the pinion gear by manipulation of the slip-operating mechanism, raising and lowering the rack cylinder and the slips in the tubing head and controlled engagement and disengagement of the coiled tubing by the slips.
A still further object of this invention is to provide a coiled tubing hanger assembly for running coiled tubing in a well, which assembly includes a specially designed tubing head having a bonnet, a midsection and a lower body, with a tapered or conical throat provided in the midsection for accommodating multiple, tapered slips assembled in a correspondingly conical configuration on a slip retainer ring and seated on a cylindrical rack cylinder located in a midsection bore communicating with the tapered throat, the rack cylinder having lands and grooves engaged by a pinion gear attached to a slip-operating mechanism. Manual manipulation of the slip-operating mechanism effects selective raising and lowering of the rack cylinder and the slips in the midsection bore and tapered throat, respectively, and selective engagement and disengagement of the slip teeth with the coiled tubing extending through the tubing head adjacent to the slip teeth. A pack-off assembly in the lower body prevents well pressure from interfering with operation of the coiled tubing hanger assembly.